Experimental validation of FE predicted fracture behaviour in thermally sprayed coatings

The fracture behaviour of a brittle coating on a substrate is not only governed by its intrinsic fracture strength, but also by a range of other parameters. In order to be able to understand (and thus predict) the fracture response, it is very important to accurately determine the key coating properties such as elastic modulus, residual stresses and fracture strength. In the present work, the fracture behaviour of three different high velocity oxy-fuel (HVOF) sprayed WC–17% Co coatings on Ti–6Al–4V substrates was studied using four-point bending with the acoustic emission technique. The key coating properties were determined experimentally and finite element (FE) models incorporating these experimentally measured properties were used to predict the cracking behaviour. It was found that the FE model was able to predict the differences in the fracture responses of the three coating types based upon differences in their mechanical properties, which in turn enabled the properties which dominate the fracture response to be identified. Moreover, the ability to predict the fracture behaviour of the coatings provided validation of the physical basis of the FE model.